Why is it necessary for multi-celled organisms like the frog and plants shown here to have specialized cells and organs.

Cells rely on diffusion and

osmosis to get the water, nutrients

and other molecules

necessary for life.

All organisms get these from their external

environment.

Internal environment - Extracellular spaces

Because multicellular organisms have fewer cells that are in direct contact with the external environment it is necessary for them to have specialized cells and organs to move them from one partof the organism to anther.

What observations can you make based on the pictures below

So where do multicellular organisms get the specialized cells they need to

maintain homeostasis?

The 100 or so cells in the

blastocyst are known as

embryonic stem cells.

Just like you are able to make many different types of bolts and screws

from one block of metal . . .

. . . all of the cells necessary

for life come from these stem cells.

. . . this process is known as cell differentiation

The shape of the cell serves an important role in how it functions.

Muscle Cells Nerve Cells

Blood Cells

Root Tissue Stem Tissue

Leaf Tissue

Epithelial cells (skin cells) like the ones in the picture above, are

tightly packed together.

How do you this works to protect our bodies?

But wait, don’t all of our cells have the same DNA in their nucleus?

If that’s so, then how can different cells have different shapes

In eukaryotic cells, DNA is packaged in the cell nucleus as chromosomes and chromosomes have sections that code for traits called genes

Regulating Gene Expression

A strand of DNA does not just contain genes. It also has a number of regulatory elements that help control how the genes function.

Some regulators help turn genes on, causing genes to be expressed, while other sections of DNA can turn genes off, or prevent gene expression.

In this way, certain genes are turned on during development causing cells to look and function in a certain way